Capture of gases emitted from power plants is an area of increasing interest. Power plants based on the combustion of fossil fuels (such as petroleum, natural gas, or coal) generate carbon dioxide as a by-product of the reaction. Historically this carbon dioxide has been released into the atmosphere after combustion. However, it is becoming increasingly desirable to identify ways to find alternative uses for the carbon dioxide generated during combustion.
One option for managing the carbon dioxide generated from a combustion reaction is to use a capture process to separate the CO2 from the other gases in the combustion exhaust. An example of a traditional method for capturing carbon is passing the exhaust stream through an amine scrubber. While an amine scrubber can be effective for separating CO2 from an exhaust stream, there are several disadvantages. In particular, energy is required to operate the amine scrubber and/or modify the temperature and pressure of the exhaust stream to be suitable for passing through an amine scrubber. The energy required for CO2 separation reduces the overall efficiency of the power generation process.
In order to offset the power required for CO2 capture, one option is to use a molten carbonate fuel cell to assist in CO2 separation. The fuel cell reactions that cause transport of CO2 from the cathode portion of the fuel cell to the anode portion of the fuel cell can also result in generation of electricity. However, conventional combinations of a combustion powered turbine generator with fuel cells for carbon separation have resulted in a net reduction in power generation efficiency per unit of fuel consumed.
An article in the Journal of Fuel Cell Science and Technology (G. Manzolini et. al., J. Fuel Cell Sci. and Tech., Vol. 9, February 2012) describes a power generation system that combines a combustion power generator with molten carbonate fuel cells. The combustion output from the combustion generator is used in part as the input for the cathode of the fuel cell. This input is supplemented with a recycled portion of the anode output after passing through the anode output through a cryogenic CO2 separator.
An article by Desideri et al. (Intl. J. of Hydrogen Energy, Vol. 37, 2012) describes a method for modeling the performance of a power generation system using a fuel cell for CO2 separation. Recirculation of anode exhaust to the anode inlet and the cathode exhaust to the cathode inlet are used to improve the performance of the fuel cell. Based on the model and configuration shown in the article, increasing the CO2 utilization within the fuel cell is shown as being desirable for improving separation of CO2.
U.S. Pat. No. 7,396,603 describes an integrated fossil fuel power plant and fuel cell system with CO2 emissions abatement. At least a portion of the anode output is recycled to the anode input after removal of a portion of CO2 from the anode output.